Backlight assemblies for digital LCD televisions have evolved in recent years. Backlight assemblies used to emit light generated by Cold Cathode Fluorescence (CCFL) tubes. These backlight assemblies consumed large quantities of power and required light guides and diffusers to eliminate differences in light density before presenting the light to the LCD panel.
LED backlight assemblies are commonplace in modern LCD televisions. LED backlight assemblies tend to fall into two categories of edge lit backlights and direct LED backlights. In edge lit backlight assemblies, LEDs inject light into a sheet composed of plastic with good optical properties. The edge lit plastic panel receives the light and changes its direction by 90 degrees and emits the light out of the front facing surface of the panel. The light is then passed through a plastic diffusor sheet and on to the LCD panel. The LCD light gates in the LCD panel are polarized such that un-polarized light will suffer degradation passing through the LCD gates. To overcome this problem, a polarizer sheet aligned to the polarization of the LCD gates is placed between the backlight diffusor sheet and the LCD panel assembly. Another sheet of plastic is generally adhered to the back surface of the LCD panel. This plastic film contains colored dots aligned with the LCD gates in the LCD panel. These dots are colored Red, Blue and Green so that colored light is presented to the LCD gates. Another polarized sheet of plastic is adhered to the front surface of the LCD panel to repolarize the light leaving the LCD panel so that it is directed in a controlled manner that enhances the viewing experience.